Bipolar diodes are widely used in different circuit applications in the automotive and industrial field. For example, in switching applications in which an electronic switch cyclically switches on and off an inductive load, a diode can be employed as a free-wheeling diode that takes over a current induced in the inductive load after the switch has been switched off.
In operation of a diode, conduction losses occur. These conduction losses are dependent on the voltage across the diode (often referred to as forward voltage VF) and the current through the diode.
Further, electrical charge (often referred to as reverse recovery charge QRR) resulting from a charge carrier plasma with n-type and p-type charge carriers is stored in the diode when the diode is forward biased and conducting a current. When an operation state of the diode changes from a forward biased state to a reverse biased state, the reverse recovery charges have to be removed from the diode before the diode is capable to block the voltage that reverse biases the diode. This process is often referred to as reverse recovery process. During the reverse recovery process, the charges stored in the diode cause a reverse current (often referred to as IRR). This reverse current resulting from charge stored in the diode multiplied by the voltage across the diode during the reverse recovery process equals the lower limit of the power losses resulting from the reverse recovery process. The time integral of these losses equals the energy that is dissipated each time the diode changes from the forward biased state to the reverse biased state.
In general, at a given current rating and a given voltage blocking capability, diodes with a low forward voltage (and low conduction losses) have a higher reverse recovery charge, and vice versa. Usually, the current rating of a diode is chosen in accordance with the highest currents occurring in an application in which the diode is implemented. A diode with a high current rating has a large chip size and has a high reverse recovery charge. When the diode operates at currents below the current rating, the diode is over-dimensioned so that at low currents relatively high losses resulting from the reverse recovery charge QRR occur.
It is therefore desirable to reduce diode losses in circuit applications.